1. Field of the Invention
This invention relates to the production of corrugated paperboard, and in particular to automated control based upon the moisture content of the paperboard components.
2. Description of Related Art
The measurement of moisture and the acquisition of moisture data is important in the manufacture of corrugated board such as that used where protection, separation, or support is required. A corrugated medium is typically formed in a machine which moistens or steams a paper web prior to passing it between two metal rollers cut with alternate flute tips and grooves which are geared to run in complement to each other. This impresses permanent parallel flutes in the paper perpendicularly to the machine direction. The flutes contribute significant rigidity and resistance to products which utilize the resulting corrugated medium.
After a corrugated medium is formed, it may be pasted or otherwise mounted to a liner to produce single-faced corrugated board. If liners are joined to both sides of the corrugated material, a double-wall corrugated board results, and if double-faced and single-faced boards are joined together, a double-wall board results. Moisture data has been found to play an important part in controlling such mounting.
The economic impetus to produce corrugated board in mass quantities has led to the development of an in-line production process for single-faced, double-faced and double-wall corrugated board. The in-line production processes have several constituent steps, including specific steps for monitoring and adjusting the temperature and moisture contents of the paper webs employed.
The ability to accurately monitor and control the various constituent steps involved in the in-line processes can yield substantial economic benefits for the manufacturer and improve quality control. However, the many operational steps employed in a commercial process are interdependent, and any one constituent step may result in a variety of distinct undesirable qualities in the final product, and oftentimes it is difficult and time-consuming to isolate the root cause of a defect in the product based merely upon routine observation of the defect. Nevertheless, machine operators have been relied on to make adjustments to these types of machines in response to observations of identifiable defects or sets of defects, based on the operator's intuition or experience. Typically, adjustments to the machine are made in iterative steps. This, of course results in waste of not only paper and adhesive, but also in lost production time.
It has been observed that perceived acceptable operating conditions lie within a fairly sizeable range of operating conditions, and a rapid determination of a narrower, more accurate operating range of conditions has been sought. The principal control steps for operating machines making corrugated paperboard focuses on the steps of preparing a liner for adhesive joinder, and a substantially different preparation of a paper web for formation into a corrugated medium. While the equipment for performing these different steps bears some similarity, it has been recognized that substantially different operating principles are needed if commercially acceptable products are to be made on a consistent, cost effective basis.